Just Found DR201!!!

[ebull]

I had posted the should I... thread about a week ago fishing for info as Hiwatts are still new to my possession. I am pleased to report, they are no longer. Here it is. Please help me figure out the red flags, concerns etc. The stats as I see them (please correct me I am still learning this beast.)
- DR201 (1976) #9610
- EL34 type. (mullards still in the pre )
- Partridges?
- HJ wiring?

My questions for forum sages?
- Is this amp wired as speaker pairs in series? It was sold to me with a dummy plug in place. I have a 4 ohm cab my instinct would be to set it at 4 ohms and only plug the cab in.
- The owner (son, of brother, of 'original buyer') claimed it was serviced and worked on by Ken Fischer. It would appears to me that there was obviously a mod done to the pre circuit. Anyone have any clues? seen this before? It looks similar to the 203 seen here... viewtopic.php?f=2&t=1258
any clues?
- Besides that, it looks like only the us cord was added to the chassis. with some rubber cement securing. Is it me or is the AC cord still tapped into the EU jack. This is super dangerous right?!?
- What are these going for these days?... I am 80% sure I am keeping it for my bass rig but I really just jumped on what I assumed was a good deal.

Any and all help/info is incredibly appreciated. He mentioned his father used to use it with two stacks... here is hoping they are still around somewhere.

[Dr.HI-TONE]

Congrats!
Partridges - Yes
HJ wiring - yes

mods early in preamp yes.
To power a 4 ohm cab. leave the dummy plug in one of the "A" jacks and plug your cab into the other "A" jack. Or use both "B" jacks as described for the "A" jacks.

The bulgin mains plug has wires soldered to it, but it is only somewhat dangerous if still wired to the mains switch............which is not pictured.

in this condition it is worth $1800 +/- $200. It is hard to speculate with much accuracy.

[mhuss]

It looks like someone added larger cathode bypass caps, probably to give it more low end response (the stock 2k2/47nF pair starts to roll off above 1000hz). It would be interesting to compare the stock and beefed up versions with a bass guitar.

Even though that rolloff frequency seems high, I've never noticed an AP Hiwatt being bass-deficient. This may have been compensated for in the tone stack design. Making the cathode caps larger also makes the preamp more prone to ugly-sounding blocking distortion, but this is more of a problem with overdriven guitar sounds, not so much with bass.

--mark

[ebull]

Thank you both very much for the reply. The amp seems to be in good enough shape to be brought back to full potential. This is the first tube amp that I have liked the sound of for bass. I am sure it will need new tubes. Any suggestions? I know this can be tricky with the fixed biasing. Other than that I need to figure out why the standby switch pops so loud when i flip it... eek.
There was a phantom squelching once or twice over the 20min round I played it. Not sure. I guess i'll just have to go over the caps and all.

If it is of interest I will document the modifications to the amp. I was planning on reversing them, but i'll see If I can get it running well with them in place, as I am really digging the sound. Looks like the cathode caps as Mhuss pointed out and the few caps added to the front end were the extent of the circuit mods. Perhaps I can make it to a Hiwatt roundup to do a side by side. Either way I am highly enjoying this amp, their collectors and this forum. Much to learn... many many thanks.

[Dr.HI-TONE]

You are very welcome!

Glad you found this place!

[OldSchoolDave]

Have you checked to make sure there's no AC voltage present at the Bulgin plug? That'd be one thing I'd address ASAP. Dr.Hiwatt is probably correct in assuming whoever wired the hard line in snipped the leads to the Bulgin farther back.

Dave

[Zells]

This is the first tube amp that I have liked the sound of for bass.

Old Hiwatts are truly wonderful for bass although a lot of speakers do not mate well with them. I really dig my DR405 and DR103s.

I am sure it will need new tubes. Any suggestions? I know this can be tricky with the fixed biasing

You have the 6xEL34 version of the DR201. My first suggestion would be a sextet of Winged C, i.e. =C=, EL34 tubes. Groove Tubes EL34M handle the Hiwatts well according to Dr.HIWATT. J/J E34L tubes, but not the standard EL34, work too. Vintage Mullards are the best option if you have a large budget.

The KT88 version of the DR201 and the DR405 have adjustable bias, but that's unfortunately not the case with any of the EL34 amps. Adjustable bias could be added by a modification...and the amp has been modded a bit already so it wouldn't likely lose value.

Other than that I need to figure out why the standby switch pops so loud when i flip it... eek.

Does this happen even when the master volume is turned down? If yes, there is certainly a loose grounding wire somewhere. I had the same issue on of my Hiwatts when a ground wire fractured on one of the posts of a filter capacitor that I replaced. I bent the ground wire at too tight an angle around the post when soldering in the new caps. I re-soldered the wire and all is well again.

It looks like someone added larger cathode bypass caps, probably to give it more low end response

Oh geez. These amps have too much low end already when the 'bass' EQ knob is turned clock-wise. The huge frequency broadband of the Partridge output transformers reaches extremely low. I typically use a 10-band EQ pedal with bass through the DR405 to cut the sub-lows (< 50 hz) and boost the low-mid frequencies (50 - 300 hz). This amp can even fart out a pair of Eminence Kappalite 3015LF PA speakers.

[ebull]

Okay,
I have finally had a moment to sit and take real look at what is going on inside this amp. Yes, the AC was cut to the bulgin plug. However, it looks like the ground wire from the new cord was tied to the ground in the bundle coming from the bulgin. As I see it, unless that grounds somewhere I cannot see, then the the bulgin plug that is not in use can ground out to the wall and everything else is still just ground to the chassis. Perhaps this could account for the popping with the standby switch? (I do still need to check if it's master volume sensitive)

As for bias and tubes. I did not think I would miss much with the el34's but biasing options seem nice now that I have read some of the issue hiwatts can have. I will probably try to gt el34m's first. My understanding is that I am looking for -38 on the biasing and if I cannot get that then I might have to explore a little bit of modding as it is 'fixed to mullards' biasing. Like I said earlier... I get electronics and have build pedals. But amp servicing is a bit new.

Zells, thank you for the help and info as well. I might PM you with some bass specific setup questions.

[riba2233]

Okay,
I have finally had a moment to sit and take real look at what is going on inside this amp. Yes, the AC was cut to the bulgin plug. However, it looks like the ground wire from the new cord was tied to the ground in the bundle coming from the bulgin. As I see it, unless that grounds somewhere I cannot see, then the the bulgin plug that is not in use can ground out to the wall and everything else is still just ground to the chassis. Perhaps this could account for the popping with the standby switch? (I do still need to check if it's master volume sensitive)

As for bias and tubes. I did not think I would miss much with the el34's but biasing options seem nice now that I have read some of the issue hiwatts can have. I will probably try to gt el34m's first. My understanding is that I am looking for -38 on the biasing and if I cannot get that then I might have to explore a little bit of modding as it is 'fixed to mullards' biasing. Like I said earlier... I get electronics and have build pedals. But amp servicing is a bit new.

Zells, thank you for the help and info as well. I might PM you with some bass specific setup questions.

Standby switch pops if tubes are not warm enough, but there could be other reasons.

You don't need to add bias trim pot, you can just add parallel resistor or change bias resistor. (somebody already added parallel resistor as you can see).